Gigou, P-Y., Lamontagne-Lacasse, M., & Goulet, E. D. (June 2, 2010). Meta-analysis of the effects of pre-exercise hypohydration on endurance performance, lactate threshold, and VO2max. Presentation 1679 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

This study investigated the magnitude of the effects of pre-exercise hypohydration (fluid loss) on endurance performance, VO2 at lactate threshold, and maximal oxygen consumption (VO2max) using a meta-analytic approach. Studies were located via database searches and cross-referencing. Inclusion criteria were: bodyweight loss incurred >one hour prior to the exercise tests; hydration level in the control group was <0.5% and >-1% bodyweight; hypohydration level in the experimental group was >1% bodyweight and >0.5% more than control. Exclusion criteria included the use of diuretics and caloric restriction-induced bodyweight loss.

Research articles (N = 29) were retrieved. Ten met the inclusion criteria for endurance performance, seven for VO2 at lactate threshold, and seven for VO2max. These provided 14, 10, and 11 effect estimates respectively. Mean bodyweight decreases in all experimental groups were ~3.9%. For endurance performance and VO2 at lactate threshold, mean exercise test times among studies was ~21 (but with considerable variation). Mean power output fell by ~3.2% and VO2 at lactate threshold by 5.63% in hypohydrated groups relative to control. Percent change in power output and VO2 at lactate threshold did not differ between studies with bodyweight losses <4% or >4%. Meta-regression analyses did not establish significant relationship patterns between bodyweight losses and percent changes in power output or VO2 at lactate thresholds. With pre-exercise hypohydration, VO2max decreased by ~2.4% compared with control groups. Percent change in VO2max in studies with bodyweight losses <4% was significantly lower than in those with bodyweight losses >4%. VO2max was found to decrease by ~2.9% for each percent loss in bodyweight above a threshold loss of 3.1%.

Implication. Pre-exercise hypohydration >3% bodyweight impairs endurance performance, VO2 at lactate threshold, and VO2max in a practically important manner. Being too dehydrated before an event can be detrimental to performance.